1. Field of the Invention
The present invention relates to an improved process for hydroformylation of olefinically unsaturated compounds using a catalyst based on cobalt and/or rhodium used in a two-phase medium. One of the phases is constituted by a non-aqueous ionic solvent comprising at least one quaternary ammonium and/or phosphonium cation Q+ and at least one anion Axe2x88x92. The catalyst comprises at least one complex of cobalt and/or rhodium co-ordinated with at least one ligand selected from the group formed by nitrogen-containing or phosphorus-containing ligands also carrying an ionic function (Qxe2x80x2)+(Axe2x80x2)xe2x88x92 where Q and Qxe2x80x2 and/or A and Axe2x80x2 are chemically identical.
2. Description of the Prior Art
Hydroformylation of olefinic compounds is a reaction of great industrial importance and the majority of processes use homogeneous catalysts dissolved in an organic phase constituted by the reactants, products and possibly an excess of ligand, although difficulties are encountered in separating and recovering the catalyst, in particular when it is used in relatively large quantities, as is the case with catalysts based on cobalt, or with a noble metal, as is the case with rhodium based catalysts.
One solution to resolving that problem has been suggested by Bartik et al.: Organometallics (1993) 12 164-170, J. Organometal. Chem. (1994) 480 15-21, and by Beller et al.: J. Molecular Catal. A: Chemical (1999) 143 31-39. It consists of carrying out hydroformylation in the presence of an aqueous solution containing a cobalt complex which is rendered water-soluble by the presence of a phosphine-sulfonate ligand such as the sodium salt of trisulfonated triphenylphosphine or a trisulfonated tris-(alkylphenyl)phosphine. International patent application WO-A-97/00 132 describes clusters of cobalt substituted by trialkoxysilylmethyl groups, which render them water-soluble. In that manner, the organic phase containing the aldehydes is readily separated from the aqueous phase containing the catalyst.
A further solution to the problem has been described in U.S. Pat. No. 4,248,802. It consists of carrying out hydroformylation in the presence of an aqueous solution containing a rhodium complex which is rendered water-soluble by the presence of a sulfonated phosphine ligand which is itself water-soluble, such as the sodium salt of trisulfonated triphenylphosphine. In that manner, the organic phase containing the aldehydes is readily separated from the aqueous phase containing the catalyst. This technique has formed the subject matter of a considerable number of studies which have been discussed in an article by W. A. Herrmann in xe2x80x9cAngewandte Chemie Internationalxe2x80x9d, 1993, volume 32, page 1524 ff.
Despite the huge industrial interest of such techniques in the hydroformylation of propylene, such two-phase systems suffer from a lack of solubility of the olefins in water, which leads to relatively low reaction rates which renders them unsuitable for long chain olefins.
Further, United States patent U.S. Pat. No. 3,565,823 describes a technique consisting of dispersing a transition metal compound in a quaternary ammonium or phosphonium tin or germanium salt with formula (R1R2R3R4Z)YX3, where R1, R2, R3 and R4 are hydrocarbyl residues containing up to 18 carbon atoms, Z is nitrogen or phosphorus, Y is tin or germanium and X is a halogen, for example chlorine or bromine. U.S. Pat. No. 3,832,391 describes a process for carbonylating olefins using such a composition. Those compositions have the disadvantage of having a relatively high melting point, for example more than 90xc2x0 C., which complicates manipulation of the solutions of catalyst and reaction products.
The Applicant""s patent U.S. Pat. No. 5,874,638 describes benefiting both from the advantages of two-phase processing and avoiding the disadvantages connected firstly with using water and secondly with using compounds with high melting points, by dissolving certain catalytic compounds of transition metals from groups 8, 9 or 10, known to catalyze hydroformylation, in non-aqueous ionic solvents which are constituted by organic-inorganic salts which are liquid at ambient temperature.
It has now been discovered that, in the hydroformylation reaction catalyzed by complexes based on cobalt and/or rhodium carried out in a non-aqueous ionic solvent comprising at least one quaternary ammonium and/or phosphonium cation Q+ and at least one anion Axe2x88x92, which catalyst is liquid at a temperature of less than 90xc2x0 C., the amount of metal retained in the ionic solvent is greatly improved when the catalyst comprises at least one cobalt and/or rhodium complex coordinated by at least one ligand selected from the group formed by nitrogen-containing or phosphorus-containing ligands also carrying an ionic function (Qxe2x80x2)+(Axe2x80x2)xe2x88x92 where Q and Qxe2x80x2 and/or A and Axe2x80x2 are chemically identical.
More precisely, the invention provides a process for liquid phase hydroformylation of olefinically unsaturated compounds in which the reaction is carried out in the presence of at least one non-aqueous ionic solvent comprising at least one salt with general formula Q+Axe2x88x92, where Q+ represents a quaternary ammonium and/or phosphonium cation, and A represents an anion, and at least one cobalt and/or rhodium complex coordinated by at least one ligand selected from the group formed by nitrogen-containing or phosphorus-containing ligands also carrying an ionic function (Qxe2x80x2)+(Axe2x80x2)xe2x88x92 where at least the cation (Qxe2x80x2)+ or anion (Axe2x80x2)xe2x88x92 has the same chemical nature as the cation Q+ or anion Axe2x88x92 of the non-aqueous ionic solvent.
The non-aqueous ionic solvent is selected from the group formed by liquid salts with general formula Q+Axe2x88x92 where Q+ represents a quaternary ammonium and/or phosphonium and Axe2x88x92 represents any anion which can form a liquid salt at low temperature, i.e., below 90xc2x0 C., advantageously at most 85xc2x0 C., preferably below 50xc2x0 C. Preferred anions Axe2x88x92 are nitrate, sulfate, phosphate, acetate, halogenoacetates, tetrafluoroborate, tetrachloroborate, hexafluorophosphate, hexafluoroantimonate, fluorosulfonate, perfluoroalkylsulfonates and arene-sulfonates, these latter optionally being substituted by halogen or halogenoalkyl groups.
The quaternary ammonium and/or phosphonium cations Q+ preferably have general formula NR1R2R3R4+ and PR1R2R3R4+ or general formulae R1R2Nxe2x95x90C R3R4+ or R1R2Pxe2x95x90C R3R4+ where R1, R2, R3 and R4, which may be identical or different, represent hydrogen (with the exception of the NH4+ cation for NR1R2R3R4+), preferably a single substituent represents hydrogen, or hydrocarbyl residues containing 1 to 30 carbon atoms, for example saturated or unsaturated, cycloalkyl or aromatic alkyl groups, or aryl or aralkyl groups, which may be substituted, containing 1 to 30 carbon atoms. The ammonium and/or phosphonium cation can also be derived from nitrogen-containing and/or phosphorus-containing heterocycles containing 1, 2 or 3 nitrogen and/or phosphorus atoms, in which the cycles are constituted by 4 to 10 atoms, preferably 5 or 6 atoms.
The quaternary ammonium and/or phosphonium cation can also be a cation with formula:
R1R2+Nxe2x95x90CR3-R5-R3Cxe2x95x90N+R1R2
or
R1R2+Pxe2x95x90CR3-R5-R3Cxe2x95x90P+R1 R2
where R1, R2 and R3, which may be identical or different, are defined as above and R5 represents an alkylene or phenylene residue.
groups R1, R2, R3 and R4 include the following radicals: methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, amyl, methylene, ethylidene, phenyl or benzyl; R5 can be a methylene, ethylene, propylene or phenylene group.
The ammonium and/or phosphonium cation Q+ is preferably selected from the group formed by N-butylpyridinium, N-ethylpyridinium, pyridinium, 3-ethyl-1-methyl-imidazolium, 3-butyl-1-methyl-imidazolium, diethylpyrazolium, N-butyl-N-methylpyrrolidinium, trimethylphenyl-ammonium, tetrabutylphosphonium and tributyl-(tetradecyl)-phosphonium. Examples of salts which can be used which can be cited are N-butyl pyridinium hexafluorophosphate, N-ethylpyridinium tetrafluoroborate, pyridinium fluorosulfonate, 3-butyl- 1-methyl imidazolium tetrafluoroborate, 3-butyl-1-methyl-imidazolium hexafluoroantimonate, 3-butyl-1-methyl-imidazolium hexafluorophosphate, 3-butyl-1-methyl-imidazolium trifluoroacetate, 3-butyl-1-methyl-imidazolium trifluoromethylsulfonate, trimethylphenylammonium hexafluorophosphate and tetrabutylphosphonium tetrafluoroborate. These salts can be used alone or as a mixture.
The cobalt and/or rhodium compound precursors of the catalyst are selected from the group formed by cobalt and/or rhodium salts such as acetylacetonates, carboxylates, in particular formate or acetate, and carbonyl compounds, such as dicobalt-octacarbonyl, cobalt-tetracarbonyl hydride, rhodium-dicarbonyl acetylacetonate and carbonyl clusters. The choice of cobalt and/or rhodium compound precursor is not critical but it is generally preferable to avoid halides.
The nitrogen-containing ligand is selected from the group formed by monoamines, di-, tri- and polyamines, imines, di-imines, pyridines, bipyridines, imidazoles, pyrroles and pyrazoles, all also containing in their formula at least one substituent carrying an ionic function (Qxe2x80x2)+(Axe2x80x2)xe2x88x92 where at least the cation (Qxe2x80x2)+ or anion (Axe2x80x2)xe2x88x92 has the same chemical nature as cation Q+ or anion Axe2x88x92 of the non-aqueous ionic solvent defined above.
The phosphorus-containing ligand is selected from the group formed by phosphines, polyphosphines, phosphine oxides and phosphites, all also containing in their formula at least one substituent carrying an ionic function (Qxe2x80x2)+(Axe2x80x2)xe2x88x92 such that at least the cation (Qxe2x80x2)+or anion (Axe2x80x2)xe2x88x92 has the same chemical nature as cation Q+ or anion Axe2x88x92 of the non-aqueous ionic solvent defined above.
Non limiting examples of associations between the ligands and molten salts which can be cited are:
1-(4-pyridyl)2-(dicyclopentyl-methyl-phosphonium)-ethane tetrafluoroborate (1) and 1-(N-imidazolyl)-2-(dicyclopentylmethyl-phosphonium)-ethane tetrafluoroborate (2) ligands, used in ionic solvents constituted by quaternary ammonium or phosphonium tetrafluoroborates and by salts comprising dicyclopentyl-methyl-alkyl-phosphonium cations;
1-(diphenylphosphino)2-(4-N-methyl-pyridinium)-ethane hexafluorophosphate (3) ligand, used in ionic solvents constituted by quaternary ammonium or phosphonium hexafluorophosphates and by salts comprising 4-alkyl-N-methyl-pyridnium cations, the 1-(dicyclopentylphosphino)2-(3-methyl-1-imidazolium)-ethane hexafluorophosphate (4), used in ionic solvents constituted by quaternary ammonium or phosphonium hexafluorophosphates and by salts comprising 3-alkyl-1-methyl-imidazolium cations; 
N-(3-diphenylphosphinophenyl)-Nxe2x80x2-dimethyl-guanidinium tetrafluoroborate ligand (5), used in ionic solvents constituted by quaternary ammonium or phosphonium tetrafluoroborates and by salts comprising N-phenyl-Nxe2x80x2-dialkyl-guanidinium cations;
tris-(tetrabutylammonium 3-phenylsulfonate)-phosphine (tetrabutylammonium triphenylphosphine trisulfonate) (6), used in ionic solvents constituted by tetrabutylammonium salts and by salts comprising sulfonate anions, such as tosylates and triflates;
tris-(sodium 3-phenyl sulfonate)-phosphine ((sodium triphenylphosphine trisulfonate) (7), used in ionic solvents constituted by salts comprising sulfonate anions, such as tosylates and triflates; 
and the ligand (di-t-butyl-3,5-catecholato)-(tetrabutylammonium 4-phenoxy-sulfonate)phosphite (8), used in ionic solvents constituted by tetrabutylammonium salts and by salts comprising sulfonate anions, for example tosylates and triflates. 
The catalytic composition is obtained by mixing, in any manner, the liquid salt with the cobalt and/or rhodium salt and the ligand. The transition metal compound and/or the ligand can initially be dissolved in an organic solvent.
The complex between the cobalt and/or rhodium precursor and the ligand can be prepared prior to the reaction by mixing the cobalt and/or rhodium precursor with the ligand in a suitable solvent, for example an organic solvent or the non-aqueous ionic solvent which will subsequently be used in the catalytic reaction. The complex can also be prepared in situ by mixing the cobalt and/or rhodium precursor and the ligand directly in the hydroformylation reactor.
The concentration of the cobalt and/or rhodium complex in the liquid ionic solvent is not critical. It is advantageously in the range 0.1 mmoles to 5 moles per liter of liquid ionic solvent, preferably in the range 1 mmole to 1 mole per liter, and more preferably in the range 10 to 500 mmoles per liter. The mole ratio between the ligand and the cobalt and/or rhodium compound is in the range 0.1 to 500, preferably in the range 1 to 100.
The components in the composition of the invention can be mixed in any order, at a temperature in the range xe2x88x9220xc2x0 C. to 200xc2x0 C., preferably in the range 0xc2x0 C. to 140xc2x0 C. and advantageously in the range 20xc2x0 C. to 90xc2x0 C.
The olefinically unsaturated compounds which can be hydroformylated are selected from the group formed by mono-olefins, di-olefins, in particular conjugated di-olefins, olefinic compounds comprising one or more heteroatoms, in particular from unsaturated groups such as ketone and carboxylic acid functions. Examples that can be cited are the hydroformylation of pentenes to hexanal and methylpentanal, of hexenes to isoheptanals, of isooctenes to isononanals and of C10 to C16 olefinic cuts to C11 to C17 aldehydes. These olefinic compounds can be used in the pure form or diluted with saturated hydrocarbons or other unsaturated hydrocarbons.
The ratio of the partial pressures of hydrogen and carbon monoxide used in the reaction medium for hydroformylation can be 10:1 to 1:10, preferably in a ratio of 1:1, but any other ratio can be used depending on the process.
The temperature at which hydroformylation is carried out is in the range 30xc2x0 C. to 200xc2x0 C., advantageously the temperature is less than 150xc2x0 C., preferably in the range 50xc2x0 C. to less than 150xc2x0 C. The pressure can be in the range 1 MPa to 20 MPa, preferably in the range 2 MPa to 15 MPa.
The catalytic unsaturated compound hydroformylation reaction can be carried out on a closed system, in a semi-open system or batchwise using one or more reaction stages. At the reaction outlet, the organic phase containing the reaction products is advantageously separated by simple decanting of the ionic solvent phase containing the xe2x80x9cmolten saltxe2x80x9d and the major portion of the catalyst. At least a portion of this ionic solvent phase, which contains at least a portion of the catalyst, is returned to the reactor, the other portion being treated to eliminate the catalyst residues.
The following examples illustrate the invention without limiting its scope.